From the viewpoint of reducing the weight of various components, a resin is used as a substitute of metal. However, there are many cases where it is difficult to substitute all the metal components with a resin. In this case, a technique of integrally bonding a metal molded article and a resin molded article to each other to manufacture a new composite component is considered. However, a technique of integrally bonding a metal molded article and a resin molded article to each other using an industrially advantageous method with high bond strength has not been put into practice.
Recently, as a technique of integrally bonding a metal molded article and a resin molded article to each other, a technique of bonding a metal member on which a fine concavo-convex portion is formed to an engineering plastic having a polar group which has affinity to the metal member is considered (for example, Patent Documents 1 to 5).
For example, Patent Documents 1 to 3 disclose techniques of dipping an aluminum alloy in an aqueous hydrazine solution to form a concave portion having a diameter of 30 nm to 300 nm on a surface of the aluminum alloy, and then bonding a polybutylene terephthalate resin (hereinafter referred to as “PBT”) or a polyphenylene sulfide resin (hereinafter referred to as “PPS”) to the treated surface.
In addition, Patent Document 4 discloses a technique of anodizing an aluminum raw material in an electrolytic bath of phosphoric acid or sodium hydroxide to form an anodic oxidation coating having a concave portion with a diameter of greater than or equal to 25 nm on a surface of the aluminum raw material, and bonding an engineering plastic to the treated surface.
Further, Patent Document 5 discloses a technique of forming a fine concavo-convex portion or a hole on an aluminum alloy using a specific etchant, and then injecting and bonding a polyamide 6 resin, a polyamide 66 resin, or PPS to the hole.
In Patent Documents 1 to 5, an engineering plastic having a polar group is used as a resin member. On the other hand, regarding a non-polar polyolefin resin not having affinity to a metal member, examples of a case to which the above-described technique is applied include an acid-modified polyolefin resin in which a polar group is introduced into a polyolefin resin (Patent Document 6). However, in order to bond the resin and a metal member to each other, it is necessary that the metal member and the resin be in contact with each other under high pressure for a long period of time in a state where the resin is melted, and the bonding is performed using a lamination method by melt extrusion, a press method, or the like. However, a lamination method, a press method, or the like has a low degree of freedom for the applicable shape and has a problem in that the performance and appearance of a metal member cannot be utilized depending on the shape of the member when the acid-modified polyolefin resin is bonded to a portion of the member other than a bonding target area.
In addition, in the related art, an oil-based coating material is used as a coating material of a metal member used for home electronics, construction materials, or automobiles. However, recently, the use of a water-based coating material has increased instead of the oil-based coating material from the viewpoints of reduction in environmental pollution, occupational health, and safety. As a coating component (resin component) contained in these water-based coating materials, for example, an epoxy resin, an acrylic resin, a polyester resin, or a polyurethane resin is used.
Examples of the coating component in the related art include an water-based dispersion composition (Patent Document 7) that is obtained by a reaction of an ethylene-unsaturated carboxylic acid copolymer and an epoxy compound; a water-based rust preventive coating composition (Patent Document 8) that includes a vinyl-based copolymer having a hydrolyzable silyl group and an aminimide group, an uncured epoxy resin, and a rust preventive pigment; a water-based resin composition (Patent Document 9) in which a modifier component containing at least one compound of a diketone compound, a keto ester compound, a ketimine compound, and a benzotriazole compound, a bisphenol type epoxy resin, and a phosphate compound are used; and a water-dispersible urethane compound (Patent Document 10) that contains a dicarboxylic acid dihydrazide compound.
However, even when a water-based coating material containing the above-described resin composition is used, coating adhesion to a metal surface is not sufficiently satisfactory.